This invention relates to a fluid suspension system for vehicles in general and, in particular, for a single-axle wheel-type tractor articulately joined with an earthmoving scraper to provide a self-propelled tractor-scraper combination.
Single-axle wheel-type tractors in tractor-scraper combinations, for example, usually employ hydraulic jacks for an elevationally adjustable suspension between vehicle frame and axle. Suspension control valves act to allow delivery of pressurized fluid into the suspension jacks when the scraper is loaded, and to cause withdrawal of the fluid from the jacks when the scraper is unloaded, thereby leveling the vehicle in both the loaded and unloaded conditions.
An objection to the prior art fluid suspension system of this type arises from the fact that the suspension control valves are mechanically linked to the tractor axle. Inevitably, therefore, the valves operate with the up-and-down motion of the vehicle during travel, resulting in the waste of the hydraulic fluid under pressure. Such unnecessary repetitive energizing of the valves materially shortens the useful life of the components making up the suspension system.
Another serious drawback of the known fluid suspension system is that it requires a pump devoted exclusively to suspension control. The tractor-scraper of the type in question demands leveling by the suspension system only when the vehicle height changes upon loading and unloading of the scraper. The function of the suspension system as a vibration absorber to take up the normal dynamic motion of the machine traveling over rough terrain can be performed by some means other than the hydraulic jacks.